In a U.S. study, early safety tests suggested the eggs of pig whipworms have anti-inflammatory properties, reducing the size of brain lesions in MS patients. A similar trial is under way in Denmark. And in Britain, academics at the University of Nottingham are studying the potential health benefits of hookworms, another type of parasitic worm.

If these trials prove successful, treatment with parasitic worms—known as helminthic therapy—could provide a simple, cheap, natural and controllable treatment for the debilitating condition, which affects 2.5 million people world-wide.

Multiple sclerosis is an inflammatory disease of the brain and spinal cord, in which an overactive immune system attacks the nerve fibers responsible for sending signals to the rest of the body. Its symptoms include impaired vision, muscle weakness and spasm, fatigue, memory loss and depression.

Medication can slow the disease's progression, but many of the drugs on the market have unpleasant side effects—including hair loss, muscle aches, fever and nausea, sleeplessness and flu-like symptoms—or more dangerous risks including organ damage and brain infection.